In recent years, attention has been focused on sheet displays. A sheet display comprises a base of a flexible material such as a polyimide film and has a characteristic of allowing a completed display element to be bent and the like. An organic electroluminescent (hereinafter simply called organic EL) element or the like is used as the display element in the sheet display.
An emitting layer included in the organic EL element is easily degraded by influence of moisture. The degradation of the emitting layer may be a reason for inconvenience such as reduction in the amount of light emission and unluminousness in the organic EL element. For this reason, a structure capable of preventing moisture from entering the organic EL element from the outside is important. For example, a technology of bonding a sealing layer formed of polyimide or the like on a heat-resistant flexible substrate formed of polyimide or the like has been proposed. The sealing layer prevents oxygen or moisture from entering from a lower portion of the flexible substrate.
Recently, influence of hydrogen atoms is considered. In particular, if a transistor which drives the organic EL element is a MOS transistor using low-temperature polycrystalline silicon, transistor characteristics may be varied and the display quality may be varied since hydrogen atoms diffuse to the channel layer and the gate insulating film.